As known, besides coining, there are essentially two production processes for making ingots, or bars, made of gold and other precious metals: a traditional method, which entails pouring the melt, i.e. molten metal, through a crucible into a mold of appropriate dimensions (the ingot mold), leaving then the melt to cool in air, making it solidify under the influence of flames generated by gas burners, or a more modern method, wherein granules, or other metal elements, are introduced in the mold and melted in a furnace, subsequently cooling the mold, and therefore also the molten metal contained therein, in a conveniently sized thermal container.
According to the more modern method, calibrated quantities of the material to be melted are initially introduced in molds with a shape that is substantially complementary to that of the ingots, or of the bars, to be provided.
The material to be melted can be constituted, for example, by grains, powder, crystals or swarf of various sizes.
The molds are thus inserted inside tunnel-type furnaces, preferably of the induction type, in which they are first heated up to the melting point of the metal and then cooled until the metal solidifies.
Recently, the more modern method has been recognized as compliant with the technical standards imposed by the London Bullion Market Association (LBMA), i.e. the trade association in the field of the professional market for ingots, for the production of so-called “good delivery” ingots.
It should be noted, however, that the LBMA also imposes that verifications of the purity level are to be performed on the produced ingots, regardless of which production process they originate from.
While there are instruments for purity verification that are well codified, and recognized also by the LBMA, for production systems that entail the use of crucibles, as regards the production of ingots melted directly in the molds, currently no instruments for purity verification are known.